1. Field of the Invention
The present invention generally relates to optical equipment assemblies and techniques, and more particularly to disc media metrology.
2. Description of the Related Art
A form of an information storage and retrieval device is a hard disc drive (“disc drive”). A disc drive is conventionally used for information storage and retrieval with computers, data recorders, redundant arrays of independent discs (RAIDs), multimedia recorders and the like. A disc drive comprises one or more disc media.
Each disc media comprises a substrate upon which materials are deposited to provide a magnetically sensitive surface. In forming the magnetically sensitive surface, a servo pattern or more particularly servo pattern media, may be formed on such substrate. A servo pattern media conventionally is a pattern of raised features, such as posts or columns. In a servo pattern, position error signal (PES) marks may be formed. Such PES marks conventionally are a pair of contiguous or inter connected posts. In addition to such servo pattern media, another form of pattern media that may be formed on a substrate is bit pattern media. A bit pattern or bit pattern media is an arrangement of posts or columns for storing bits of information.
As disc media storage requirements increase, namely, density is enhanced, topographic features whether for servo pattern media, bit pattern media or other media become smaller. For example, PES marks in bit patterns may be formed below 500 nanometers in lateral dimension. Moreover, as such posts become smaller in lateral dimension, spacing between posts also decreases. Thus, viewing such posts, as well as regions between posts, by conventional means is not practical. For example, a conventional interference based microscope uses a monochromatic light source of approximately 550 nanometers. Because the wavelength of the light source is larger than lateral dimension of the bit pattern elements themselves, a conventional interference based microscope is not sufficient for detailed resolution of topographic information associated with such pattern media.
Accordingly, an atomic force microscope (AFM) may be used to scan a disc media surface. An AFM scans not optically, but by physical touch using a contact probe. However, a difficulty arises in locating patterns for identifying a correct contact starting position for an AFM scan. Conventionally, a technician uses an interference-based microscope to locate a pattern; however, as mentioned above owing to limitations of such conventional interference-based microscopes placement of probe tip is problematic. It should be appreciated that an AFM probe tip may be as narrow as 1 nanometer. Accordingly, it would be desirable to provide method and apparatus to detect servo patterns. Moreover, it would be desirable to provide method and apparatus to detect servo patterns for determining a starting position for an AFM scan in order to obtain an nano-scale topographic image or other topographic information.
Not all servo pattern media uses topographic features. Some servo patterns are magnetically written. Conventionally, magnetically written servo patterns do not have topographic features. This is because rather than relying on spacing loss to generate a differential signal as in topographically patterned surfaces, magnetically written patterns use magnetic signal. Accordingly, it would be desirable to provide method and apparatus to detect servo patterns whether topographically or magnetically produced.